- Zakura, the team behind a newer version of the Zcash software, has proposed giving every ZEC swap made through NEAR Intents its own viewing key, closing a gap a future quantum computer could exploit.
- The gap arises from how refunds work. When someone swaps private ZEC through the service, one of their private Zcash addresses is posted on NEAR’s public chain so unused funds can be returned, and it stays there permanently even when no refund is needed.
- What that exposes is history rather than money. Zcash wallets generate many addresses that typically share a single viewing key, so an attacker able to recover that key from one published address could link every payment the account ever received and read the amounts and attached memos. Spending requires a separate key, so the funds themselves remain safe.
- Independent evidence has strengthened the concern. Google said last week its Willow quantum chip produced near-perfect versions of one component such an attack would consume, a step toward a machine capable of running Shor’s algorithm, published in 1994 for exactly this purpose.
What Happened?
Zakura’s design leaves the spending key with the user’s main account, so an attacker cracking a single refund address would see only the payments tied to that one swap. It also addresses a practical difficulty: a wallet with hundreds of swaps would hold hundreds of keys, and restoring from backup would require scanning the entire chain with each. The answer is a database the wallet queries using private information retrieval, so it can ask where its refunds landed without the database learning which addresses it asked about. Wallets built on Zakura’s open-source libraries, including Vizor, could add the feature within weeks, with hardware wallets following once firmware supports it, ahead of a January target Zcash developers set for quantum-resistant payments. No quantum computer capable of recovering these keys has been demonstrated.
Why It Matters?
The distinction between losing money and losing privacy is the point most quantum coverage misses, and it changes what the risk means for different assets. For bitcoin, where Satoshi-era public keys sit openly onchain, a sufficiently powerful machine means theft. For Zcash, the spending key is separate, so the funds stay put while the entire transaction history becomes readable, including counterparties, amounts and private memos. For an asset bought specifically for confidentiality, retrospective disclosure may be the worse outcome, because coins can be moved to safety while a revealed history cannot be made private again. Anyone holding privacy assets should understand which of the two risks applies to them. The harvest-now, decrypt-later problem is the uncomfortable corollary. Addresses already posted to NEAR’s public chain are permanently recorded, and a machine built years from now can work backward from data captured today. Zakura’s fix limits the damage from future swaps; it does nothing about what has already been published. That asymmetry applies across the industry and argues for acting before any timeline is confirmed rather than after. On the evidence, the Google result deserves weight precisely because Google sells no quantum-resistant crypto products. When nine companies that sell such products formed an alliance last week warning about this risk, the commercial interest was worth noting. A chip result from a research lab with no stake in the outcome is a different kind of data point, and it makes the concern harder to discount as vendor messaging.
What Next?
Wallets using Zakura’s libraries could implement this within weeks, with hardware wallets dependent on firmware updates, ahead of the January target for quantum-resistant payments. Watch whether other privacy-focused networks adopt comparable per-transaction key schemes. The Google Willow trajectory is the independent variable determining urgency, and further results there matter more than any industry timeline. For bitcoin the separate question remains whether vulnerable coins get moved, frozen or left alone, and that is a governance decision rather than a technical one.
Affected Tickers and Coins: ZEC, NEAR, BTC, ETH, USDC
Source: CoinDesk
